Means for producing electrical oscillations



May 26,\1925.

1,539,402 H. W. NICHOLS MEANS FOR PRODUCING ELECTRICAL OSCILLATIONSFiled Feb. 24, 1919 by MW Patented May 26, 1925. v

UNITED STATES PA 1,539,402: TENTOFFICE.

HAROLD W. NICHOLS, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC.TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A GOjR-PORATION OF NEWYORK.

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Application filed February 24, 1919. Serial No. 278,573.

To all whom it may concern:

Be it known that I, HAROLD W. lflioiions, a citizen of the UnitedStates, residing at Maplewood, in the county of Essex, State of NewJersey, have invented certain new and useful Improvements in Means forProducing Electrical Oscillations, of which the following is a'full,clear, concise, and exact description.

. his invention relatesto means for producing electrical oscillations.More particularly, it relates to the means for controlling the frequencyof the oscillat ons produced by generators of the feedback or reactionamplifier type.

The object of the invention is to provide an oscillator havingnon-resonant means for determining the frequency of the oscillationsgenerated.

i It is well known that if the output c rcuit of an amplifier beconnected with the input circuit, of the same amplifier, or if means beprovided for feeding back energy from the output to the input circuit,oscillat ons will result if certain necessary condit ons are present.Ordinarily, an electric discharge amplifier having its output c rcuitreactively coupled to its input circuit is used, and the frequency ofthe oscillations generated is determined by, the tuning of acircuitwhich may comprise parts of either the input circuit, the outputcircu t, or both. Where a tuned circuit is not provided, theoscillations will have a frequency depending upon the capacity of thetube itself and the associated capacities and inductances.

According to the present invention, the output circuit of an amplifier,preferably a thermionic device, is arranged to feed back energy to itsinput circuit, the output and input circuits both having only one kindof reactance. There is accordingly no resonant or oscillatory circuit,and the frequency of the oscillations is determined by the value of thevarious constants of the circuit and the amplifyingtube, as willhereinafter appear. Such a device may be termed a noni-esonantoscillator.

In the accompanying drawing1 repre sents the container, preferablyhighly exhausted, having the usual hot cathode 2, impedance-controllingelement 3 and anode 4. A source 5 may supply heating current tofilamentary cathode 2. The space current or output circuit comprisescathode 2, inductance L constituting the primary of a trans former,space current source 6 and anode 4. he input circuit comprises cathode2, inductance L which is inductively coupled to inductance L polarizingsource 7 and impedance-controlling element 3. Polarizing source 7 is notessential and may be omitted. A resistance R, is connected in shunt toinductance L of the input circuit. An asym metrically conductingamplifier 10, preferably of the thermionic type, has an input circuitconnected by leads 8 and 9 across the terminals of output inductance LThe output circuit of amplifier 10 includes the primary Winding 11 of atransformer, the secondary winding 12 of which is connectttl totransmission conductor'or work circuit.13. The input circuit ofamplifier 10 may contain a polarizing source 14.

The physical process occurring is as follows:

Suppose the space current circuit 2, L 6, 4 is suddenly-closed. Thecurrent in this circuit will at first increase rapidly and anelectromotive force will be induced by L in winding L thus bringing theimpedance control element 3 to a more positive potential with respect tothe cathode 2. This causes further increase in the space current andconsequent increase in the potential of the control element, theseincreases, however, being at a slower rate as the space currentapproaches its limiting value, as determined by the impedancecharacteristic of the thermionic amplifier. Finally, a point is reachedat which the rate of space current increase is so small that theelectromotive force induced in the input circuit is less than before andthe potential of the controlling element or grid accordingly begins tofall. Falling grid potential causes the space current to begin todecrease and the decrease of space current in coil L is accompanied byan induced electromotive force in 0011 L tending to make the grid stillmore negative. In this manner the space current decreases to a minimumvalue, when it finally is caused to increase again by a reversal in thechanges of grid potential. These reversals inthe action of theimpedance-control element continue indefinitely if the various constantsofthe network including the tube and its as sociated circuits areproperly chosen, The space current, through inductance L accordinglyrises and falls cyclically in value.

Y asse ses v Any suitable means may be used for transferring to a workcircuit the alternating component of the space current energy.

As illustrated in the drawing, the input circuit of an asymmetricthermionic amplifier 10 is connected directly across the inductance L,,and the output circuit of am plifier 10 will therefore supply amplifiedoscillations to work circuit 13 by means of transformer 11, 12. Thepolarizing source 14 may be used to prevent leak current in the inputcircuit of amplifier 10. The amplifier 10 is a potential-operated deviceand acts as an infinite resistance and infinitesimal capacity in shuntto the winding L The frequency of the oscillator is independent of anyoscillatory circuits or of-electrical tuning as it is commonlyunderstood. Such an oscillator is therefore entirely different in thematter of its frequency control from those in which both the stiffnessand inertia factors'determine the generated frequency.

Viewed broadly, the input and output circuits are typical of any energytransfer system in which the capacity or potential energy storage factoris negligible, and the amplifier acts as a valve under the control ofsaid system to permit the periodic transfer of energy from a primarysource of energy, such as source 6, to said system. Potential energystorage factor is a general term used to designate the capacity of asys- ,tem, whether such capacity is due to the physical relation of theelements of the system, such as the wiring between individual pieces ofapparatus, or due to a condenser as conventionally understood.

It is not essential that the amplifier be a vacuum tube device sinceanyasymmetric mutual impedance arrangement may be used. Byasymmetricmutual impedance is meant an impedance in which the inputandoutput circuits or elements have such mutual relationship that theimpedance of one is directly dependent upon some characteristic pf theother, the impedance of the other being substantially independent of theconditions or characteristics of the one which it controls. Such animpedance may of course where I is the instantaneous current in the meshR L The potential '0 of the impedance-controlling member with respect tothe cathode may be considered as producing a cm'responding variation Vin the effective output electromotive force which will be equal to thepotential 4) multiplied by the amplifying constant p. of the amplifiergiv- D (2) V p/l). From and (2) it follows vzuIt I The differentialequation or characteristic for the above circuit may be written asfollows:

d (it the differential operator, 1,, represents the instantaneous valueof space current, R, the internal impedance of the tube between thespace current electrodes 2 and 4 and m the mutual inductance between L,and L The quantity V is negative in the second member of the equationfor the reason that a variation of potential in the input circuit isattended with a corresponding output variation electromotive force ofthe opposite sign. In other words, as the potential of the cathode 2with respect to impedance-control element 3 is increased, the effectivepotential of cathode 2 with respect to anode 4 is proportionallydecreased.

The differential equation for the closed branch R L of the input circuitmay be written as follows:

L227I1+R2I1 777'I7I2:O Rewriting (4) and (5) respectively- 1(l" 2 p)+ 2(1p+ 1) and 1( 2+ 2I 2( l The criterion for a real solution of (6) and(7) for I and I isp 2 p) :0 The general solution of equations of theform of (6) and (7 for I and I will take the form:

The real quantity 6 represents a damping factor.

For sustained sinusoidal oscillations, the general equation (12) I=e"'holds true.

Differentiating (12)- (13) pl=we =wI and (14) pzc) Trom (11) it will beseen that in the case of sustained oscillations where the damping factoris zero (15) 0),:ifl and since from (14) Hence it appears thatoscillations will be obtained when the resistances,'inductances andmutual inductance of the circuit, and the internal resistance andamplifying power of the tube are related as in (18) and the frequencyproduced by the oscillator will depend upon the resistances, inductancesand mutual inductance as shown by (20).

It should be noted that although the elements of the tube may constitutea small capacity, this plays no essential part in determining thegenerated oscillation frequency, especially at low frequencies.

Although the invention has been described and illustrated in thepreferred form only, it is to be understood that it is not to be limitedexcept as indicated by the scope of the appended claims.

What is claimed is:

1. An oscillation generator comprising a work circuit, an amplifierhaving input and output circuits, and a network of negligible capacityelectrically associating said circuits to connect the output circuits inaiding relation to the input circuit, said network and circuitsdetermining the frequency of the generated oscillations substantiallysolely by virtue of the resistance and inductance thereof.

2. An oscillator comprising a network, an amplifier associatedtherewith, said network comprising means whereby the network andamplifier transfer energy cyclicall to each other at a predeterminedperiodicity determined substantially solely by the resistance and1inductance of said amplifer and net- WOl'i.

3. A thermionic oscillation generator having an input circuit, an outputcircuit, and means to connect said output circuit in energy transferrelation to said input circuit, said circuits and connecting meanshaving a negligible amount of capacity, the frequency of the generatedoscillations being determined by the other electrical constants of saidcircuits and connecting means.

4. An oscillation generator comprising an amplifier and means forfeeding back energy amplified by said amplifier to be reamplified, bothsaid amplifier and said means haw ing negligible capacity, the frequencyof the generated oscillations. being determined by the other electricalconstants of said amplifier and energy feeding back means.

5. An oscillation generator comprising an amplifier having input andoutput circuits,

said circuits together with said amplifier constituting a network fordetermining the frequency of the generated oscillations independent ofany electrical capacity thereof.

6. An oscillation generator comprising a network, a prime source ofenergy, means whereby said source transfers energy periodically to oneportion of said network and said. portion simultaneously transfersenergy to a second portion of said network the first energy transferbeing under the control of said second energy transfer and theperiodicity of said energy transfer action being determinedsubstantially solely by resistance and. inductance.

7. A reactive network adapted to transfer energy cyclically at apredetermined periodicity, said network having electrical constants ofsuch value that the sum of the even power terms of the differentialoperator in its characteristic is zero and being nonresonant at saidpredetermined periodicity.

8. An oscillation generator comprising an amplifying device, andanetwork connected thereto, said network comprising resistance andinductance for determining the fre quency of the oscillations generated,said network being non-resonant at frequencies of the order of thegenerated oscillations.

In witness whereof, I hereunto subscribe my name'this 17th day ofFebruary A. D

HAROLD V. NI OHOLS.

